Re: [PATCH v3] drm/virtio: Add option to disable KMS support

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Am 27.02.23 um 19:15 schrieb Rob Clark:
On Mon, Feb 27, 2023 at 9:57 AM Dmitry Osipenko
<dmitry.osipenko@xxxxxxxxxxxxx> wrote:

On 2/27/23 20:38, Rob Clark wrote:
+             /* get display info */
+             virtio_cread_le(vgdev->vdev, struct virtio_gpu_config,
+                             num_scanouts, &num_scanouts);
+             vgdev->num_scanouts = min_t(uint32_t, num_scanouts,
+                                         VIRTIO_GPU_MAX_SCANOUTS);
+             if (!vgdev->num_scanouts) {
+                     /*
+                      * Having an EDID but no scanouts is non-sensical,
+                      * but it is permitted to have no scanouts and no
+                      * EDID (in which case DRIVER_MODESET and
+                      * DRIVER_ATOMIC are not advertised)
+                      */
+                     if (vgdev->has_edid) {
+                             DRM_ERROR("num_scanouts is zero\n");
+                             ret = -EINVAL;
+                             goto err_scanouts;
+                     }
+                     dev->driver_features &= ~(DRIVER_MODESET | DRIVER_ATOMIC);

If it's now configurable by host, why do we need the

Because a kernel config option makes it more obvious that
modeset/atomic ioctls are blocked.  Which makes it more obvious about
where any potential security issues apply and where fixes need to get
backported to.  The config option is the only thing _I_ want,
everything else is just a bonus to help other people's use-cases.

I find this very vague. What's the security thread?

And if the config option is useful, shouldn't it be DRM-wide? The modesetting ioctl calls are shared among all drivers.

Best regards


Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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